Concrete constructions are normally provided with some kind of reinforcement to increase the strength and to prevent cracking. The reinforcement can be single reinforcement bars (rebars), reinforcement grids or different kinds of fibres or other. Most common are reinforcement grids made from reinforcement bars of steel when larger areas are to be covered. For smaller areas or as a complement to the grids, single reinforcement steel bars are used.
To achieve the required properties in a construction, the reinforcement is placed at different heights. This height creates a concrete cover around the reinforcement in the finished construction. Reinforcement spacers are used to simplify the work of positioning the reinforcement at the prescribed height and to maintain it there through the process until the concrete has burned. The type of spacer used is influenced from e.g. regulations, the surrounding environment, natural resources or aesthetic opinions.
The concrete cover is defined as the smallest distance between the reinforcement material and the concrete surface of the completed construction. A concrete cover which differs from the requirements can negatively affect the strength and life cycle of a construction. The requirements on a concrete cover can be set by national regulations and may vary depending on type of construction and on the surrounding environment. One purpose of the concrete cover is to prevent moisture to reach the reinforcement steel, in order to avoid the negative effects corrosion has on the construction. Corrosion will, through its expansion, slowly break apart the nearby concrete, which causes more moisture to reach the steel which in turn accelerates the corrosion process. Over time this will weakens the construction strength.
To provide support for the reinforcement, reinforcement spacers are used. These are often made from plastic and are designed to facilitate that the concrete fully embraces the reinforcement and the spacers. Air pockets in the final construction must be avoided. Depending on the shape of the spacer, it must be provided with some kind of apertures in order to provide escape ways for air to disappear when concrete is poured upon them.
Reinforcement spacers are made from different materials. Most common are spacers made from plastic, but steel, concrete and other materials are also used. Plastic spacers have several advantages compared to other materials, such as ease of handling, low weight and generally low price, the manufacturing process is fast and spacers can easily be formed to a desired shape. Concrete spacers can be used in most constructions. However, the material makes them heavy and the design makes them more complicated to work with. They are primarily used when plastic is not allowed. Steel spacers are primarily used as spacers inside constructions, e.g. between two layers of reinforcement grids. Steel spacers are seldom used on a ground surface as this will cause corrosion problems.
Depending on the field of application, reinforcement spacers are divided into two main groups, foundation spacers and wall spacers. Foundation spacers are primarily used for positioning reinforcement in foundations/ground plates, while wall spacers are primarily used for positioning reinforcement in walls and vaults. The main difference is the type of underlying surfaces that they are intended to be used on.
Wall spacers are designed with thin legs and/or small feet. The formwork surface is generally hard and even, being a mould, which helps to prevent the spacer to tip over or to cut through the surface. When the formwork is removed, the spacer feet are made visible. At a wall or vault not further processed, these feet will show in the wall surface, which is not desirable. Therefore wall spacers are designed with minimal feet and are also nearly always coloured like the surrounding concrete. Low visibility is a major requirement.
Foundation spacers are designed to be used when the formwork surface is classified as soft and/or uneven, such as a bedding of coarse sand, gravel, grit or other free-draining material or ground. The bearing surface of the spacer towards the ground has a relatively large area and often a large diameter to aid the spacer to stand stable on the ground and not to dig in to the ground or to tip over. Since foundation spacers primarily are used for ground plates and foundations, the spacer will point downward and will not be visible. Foundation spacers thus have no aesthetic significance. It is important that the base plate area of the foundation spacer is large enough not to punch the underlying surface and that it minimizes the risk of the foundation spacer tipping over.
Foundation spacers are divided into two subgroups due to differences in design and the way they are used. One type is referred to as ground spacers. These typically have a large base plate and a smaller support area at the top. Due to the small support area, each spacer has to be placed in an exact position to support any reinforcement. Ground spacers are seen as cheap but time consuming to work with. The other type is linear spacers. They are long and narrow. They support the reinforcement anywhere on its support area lengthwise and no exact positioning is thus required. Due to their length, often 2 meters, they shorten the working time of placing the spacers.
Both these types of foundation spacers are positioned manually on the supporting ground, where ground spacers must be placed with an exact position. Linear spacers are often provided in 2 meter lengths and are often placed next to each other lengthwise. They are relatively heavy.
U.S. Pat. No. 6,775,954 describes a linear foundation spacer comprising three parts that must be assembled before use. AU 2006100538 describes a linear wall spacer, having small feet adapted for the use as wall spacer. A specific base segment can be attached to the feet, such that the spacer can be used as a foundation spacer. U.S. Pat. No. 4,942,714 describes a linear wall spacer. US 2005005564 describes a stackable foundation spacer having an upper receiving section for fixedly retaining of a wire mesh or single reinforcement bars.
DE 2821078 describes a circular wall spacer adapted for producing prefabricated wall modules, where the spacer can be placed randomly on the mould. With a diameter larger than a single square in a reinforcement grid, the spacer will always give support regardless its position. As most wall spacers, the legs and feet are thin, which makes it unsuitable for use on soft underlying formwork surfaces like soil or insulation, such as EPS (extruded polystyrene). The small feet will sink down in the support surface from the weight of the reinforcement and the workers walking upon it, giving an incorrect concrete cover. DE 2809430 also describes a similar wall spacer that can be positioned randomly.
There is thus room for an improved foundation spacer.